This invention relates to testing apparatus for mechanical power sources as, for example, vehicles, and to various facets of such testing apparatus.
Manufacturers of quality mechanical power sources almost invariably test the source prior to releasing the same for sale to ensure that the source is performing properly and up to its rated capability. In some cases, the testing has been performed with dynamometers, while in others, the testing has been performed by other means.
Dynamometer testing is generally preferred over other forms of testing by reason of an increased reliability of test results due to the elimination of subjective judgment on the part of operators and/or observers through the use of measuring apparatus. However, dynamometer testing is not altogether satisfactory, particularly where the mechanical power source being tested is operated at a relatively low speed and/or has a high torque output. For example, in crawler-type vehicles, where the testing is to be performed at the final drive, rotational speeds of 100 rpm or less and high torque outputs are invariably present. Conventional dynamometers cannot adequately measure desired operational parameters in such cases, or, if capable, are extremely costly thereby discouraging their use.
As a result, testing of power sources such as crawler-type vehicles has generally been performed on a test track under the control of an operator. The test results therefore can be unreliable due to the subjectivity involved, i.e., the opinion of the operator during the testing procedure, and the results will frequently vary from one operator to the next.
These difficulties are considerably compounded where the power source is a vehicle of the type having power outputs, each of which is independently driven through a hydrostatic transmission or the like. Even though the components for each output may be nominally matched, small differences in the hydraulic system for each output will exist unless a time consuming matching of components is made prior to their assembly into a given vehicle. Because of the expense involved, such a matching is not commercially feasible with the consequence that the operator of the vehicle during the test must observe any tendency of one system to perform more efficiently than the other when commanded to perform identically. If the mismatching is not perceived, when the vehicle is operated by a purchaser, continuous corrective action may be required during vehicle operation to cause the same to move in a straight line, for example, as well as during other operational procedures.
Moreover, many testing systems designed to eliminate the subjectivity involved with purely human testing on a test track or the like require time-consuming setup procedures in affixing the testing equipment to the power source or the vehicle to be tested and/or utilize space consuming, relatively mechanically complex, coupling devices, as treadmill type structures. Such structures are not only expensive, but by reason of their mechanical construction, are subject to periodic breakdown. In some cases, such structures may themselves absorb a sufficient amount of power from the source being tested as to render the test results unreliable.